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Message-ID: <Zh5Zj35zeobGGzKj@libra05>
Date: Tue, 16 Apr 2024 19:57:19 +0900
From: Yewon Choi <woni9911@...il.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Jiri Slaby <jirislaby@...nel.org>, linux-kernel@...r.kernel.org,
linux-serial@...r.kernel.org
Cc: "Dae R. Jeong" <threeearcat@...il.com>,
syzbot+6e3e8f30f269f5028e5d@...kaller.appspotmail.com
Subject: tty: n_gsm: race condition in gsmld_ioctl
Hello,
memory leak in gsmld_ioctl was reported by syzbot, and this issue seems to be
raised from race condition involving gsm->dlci[addr].
https://syzkaller.appspot.com/bug?extid=6e3e8f30f269f5028e5d
When dlci object is checked and initialized in gsmld_ioctl(), it may be
assigned multiple times because there is no lock which guards entering
the critical section in gsm_dlci_alloc() from multiple threads.
For example, when multiple ioctl() are called concurrently, the following
scenario is possible:
Thread 0 Thread 1
ioctl(GSMIOC_SETCONF_DLCI) ioctl(GSMIOC_GETCONF_DLCI)
gsmld_ioctl(): gsmld_ioctl():
dlci = gsm->dlci[addr];
dlci = gsm->dlci[addr];
if (!dlci) {
gsm_dlci_alloc(gsm, addr):
...
gsm->dlci[addr] = dlci;
if (!dlci) {
gsm_dlci_alloc(gsm, addr):
...
// overwritten & memory leak
gsm->dlci[addr] = dlci;
We think either (1) gsm_dlci_alloc() should hold a lock(mutex) and do
internal check about whether gsm->dlci[addr] is NUll or not, OR
(2) all callers of gsm_dlci_alloc() should hold gsm->mutex and check
whether gsm->dlci[addr] is NUll or not (like gsmtty_install()).
Could you check this? If it makes sense, we will write a patch following
one of the suggestions.
Best Regards,
Yewon Choi
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